Thanks Marco, that's good information.
18kg in a month is a heck of a fast rate of weight loss, and my bet is that most of that would have been water and muscle. After that you obviously settled down to a close-to-maintenance level of calories, and it sounds as if you've had no ill effects overall. You've certainly achieved a low level of body fat, which is no mean feat.
Rather than pontificating, though, I'm hoping someone with some medical / nutritional knowledge might step in with more informed comments than I can give.